it could be the shift solenoid but on your car this is not something you replace with the transmission still in the car; so I'd suggest you have a transmission shop drop the pan and inspect for metal debris and if none, then have them change the filter and carefully check that the filter seal is not damaged. The button it up and see if that helped. If not, it's trans out to replace the solenoid. The trans shop may be able to extract a trouble code from the car's computer to find out what's going on.
So it could be a very clogged filter, yes, or a shift solenoid, or internal damage to the transmission. No way to know without further diagnostics and inspection.